Method for Producing a Copper Alloy Having a High Damping Capacity

ABSTRACT

The invention relates to a copper alloy which is used for mechanically stressed components which, during operation, are subjected to vibrations and/or impacts to produce the same, and have particularly good mechanical damping properties. The composition of said copper alloy depends upon the utilisation temperature or working temperature of the component. Said copper alloy consists of 2-12 wt.-% manganese, 5-14 wt.-% aluminum and individually or in total 0-18 wt.-% of one or several elements, nickel, iron, cobalt, zinc, silicon, vanadium, niobium, molybdenum, chromium, tungsten, beryllium, lithium, yttrium, cerium, scandium, calcium, titanium, phosphorous, zirconium, boron, nitrogen, carbon, whereby each element does not contain more that 6% and 100 wt.-% copper. The alloy is obtained by adapting the martensite-austenitic conversation temperatures or the associated intervals M S -M F  and/or A S -A F  to a predetermined utilisation temperature or working temperature of the component by varying the weight proportion of the above-mentioned alloy component during melting thereof. The damping can reach above 70%.

The invention relates to a process for producing a copper alloy which is particularly suitable for components which are mechanically stressed, for example by vibration, shock or impact and has alloy properties which are matched to the intended use of the components, especially specifically improved or optimally set mechanical damping. The invention further relates to such an alloy having a particular composition and possible uses of the alloys obtained by the process.

Metallic materials or alloys having a high damping capacity are known in principle and are also referred to as HIDAMETs (HIgh DAmping METals).

A high mechanical damping capacity is desirable, for example, for reduction of vibrations and for noise damping. Such alloys are therefore particularly suitable for producing ships' propellers and pump housings and for use in vibrating machines and for preventing malfunctions caused by vibration in the case of various precision apparatuses and electronic instruments. In addition, the alloys have not only a high wear resistance but are suitable for use in various tools which are subjected to vibrations and/or impacts during operation, for example punches or dies in the shaping of sheetmetal or in lathes and milling machines.

Many HIDAMETs which can be used for noise damping and for absorption of vibrations are known. However, the fields of use of most of these materials, in particular magnesium and magnesium alloys, are seriously restricted by their unsatisfactory mechanical and corrosion properties.

HIDAMETs which display martensitic phase transformations are of particular importance in the prior art for achieving good damping properties. Alloys which display martensitic phase transformations have a different arrangement of atoms in the solid state at high temperatures than at low temperatures. The hightemperature phase is referred to as “austenite” and the low-temperature phase is referred to as “martensite”. The transformation of austenite into martensite occurs on cooling the material from the austenitic state and commences at the martensite start temperature M_(S). The martensitic transformation is concluded on reaching the martensite finish temperature M_(F). The transformation of martensite into austenite takes place on heating the material from the martensitic state, commences at the austenite start temperature A_(S) and is concluded on reaching the austenite finish temperature A_(F). In general, the damping in the martensite range (T<M_(F)) is higher because of the very much higher defect density than in the austenite range (T>A_(F)).

The best-known alloys of the type mentioned are Ni—Ti alloys (“Nitinol”), Cu—Zn—Al alloys (“Proteus”) and Mn—Cu alloys (“Sonoston”). However, these three types of alloys have disadvantages which substantially restrict their possible applications. Ni—Ti alloys have to be produced in a complicated fashion under reduced pressure and are also very expensive because of the participating alloying elements. Compared to Nitinol, Cu—Zn—Al alloys are significantly cheaper. The limited corrosion resistance and the tendency to display brittle fracture are significant disadvantages of these alloys. In addition, they are extraordinarily prone to aging both in the austenitic state and in the martensitic state. The widely used Mn—Cu alloys were developed specifically for producing ships' propellers. Due to the relatively wide solidification range of about 130° C., these alloys display a strong tendency to hot crack formation. In addition, aging effects also occur here, so that the damping effect is significantly reduced after storage for about 1000 hours at room temperature.

The patent text U.S. Pat. No. 3,868,279 discloses high-damping Cu—Mn—Al alloys and a possible way of improving their damping properties by means of heat treatment. These ternary alloys comprise 32-42% by weight of Mn, from 2-4% by weight of Al and Cu as balance, with the Mn content preferably being 40% and the Al content preferably being 2-3%. These alloys are cold rolled and subjected to heat treatment at temperatures in the range from 649° C. to 760° C., quenched in water, subsequently aged at from 204° C. to 482° C. for from 1.5 to 24 hours and cooled in air. A significant improvement in the damping properties combined with reduced brittleness compared to the previously known Heusler alloys is described.

An industrially interesting alternative to the above-described HIDAMETs are Cu—Al—Mn shape memory alloys. These materials, too, display a thermoelastic martensitic transformation. The U.S. Pat. No. 4,146,392 describes Cu—Al—Mn shape memory alloys which comprise copper as main constituent and from 4.6 to 13% by weight of manganese and from 8.6 to 12.8% by weight of aluminum as alloying constituents and have a good resistance to aging. These are alloys whose austenite-martensite transformation takes place at temperatures below 0° C. and whose shape memory effect is exploited to produce, for example, pipe connection elements.

DE 2055755 discloses a process for producing articles composed of copper-based alloys which are able to change their shape when the temperature changes. The alloys proposed for this purpose comprise copper and aluminum together with, for example, an additional element from the group consisting of zinc, silicon, manganese and iron.

Despite the very advantageous combination of mechanical properties and martensitic transformation temperatures which can be achieved, the use of Cu—Al—Mn shape memory alloys for noise- and vibration-damping materials has hitherto not been considered, since the mechanical damping properties have hitherto not been able to be set in a targeted fashion and sometimes even fluctuated greatly from batch to batch.

It was therefore an object of the invention to provide high-strength and corrosion-resistant HIDAMETs having a high damping capacity which can be reliably set in the temperature range critical for the planned use and a process for producing them.

The object of the invention is achieved by a process for producing a copper alloy having specifically improved mechanical damping, in particular for mechanically stressed components, which is characterized by the following steps:

-   -   a) a composition for the alloy is selected and the constituents         are melted in a customary way at a suitable temperature,     -   b) during this melting, at least one of the martensitic and         austenitic transformation temperatures M_(S), M_(F), A_(S) and         A_(F) is determined on a sample taken from the melt,     -   c) these transformation temperatures are increased or reduced on         the basis of a predetermined use or working temperature of the         component by targeted addition of at least one constituent of         the alloy and thus matched to the use or working temperature,     -   d) the new transformation temperatures and, if appropriate,         ranges are checked by means of a further sample and     -   e) the alloy is cast into the desired mold.

Steps c) and d) can be repeated as often as necessary until the desired matching of the transformation temperatures or ranges has been achieved.

The composition of the alloy is selected from among the constituents:

-   -   from 2 to 12% by weight of manganese,     -   from 5 to 14% by weight of aluminum and,     -   individually or together,     -   from 0 to 18% by weight of one or more of the elements nickel,         iron, cobalt, zinc, silicon, vanadium, niobium, molybdenum,         chromium, tungsten, beryllium, lithium, yttriium, cerium,         scandium, calcium, titanium, phosphorus, zirconium, boron,         nitrogen, carbon,     -   but each element in an amount of not more than 6%, and     -   copper to 100% by weight.

The alloys obtained by the process of the invention are otherwise produced by conventional melting and casting processes. The alloy can be used not only as a casting alloy but also as a forging alloy. The alloy can be shaped cold or hot. The alloys described here are particularly advantageous for all applications in which a high mechanical damping capacity is important, i.e. in particular for mechanically stressed components, instruments or housings which are subjected to vibrations, impacts or shocks.

The alloys differ from Sonoston in their considerably higher aluminum contents and significantly lower manganese contents. The high aluminum content improves the strength of the material according to the invention and at the same time increases its resistance to abrasion, erosion and cavitation. The reduced manganese concentration has a positive effect on the casting properties of the alloy because it reduces the solidification range. Dense, oxide-free and hot-crackfree castings can thus be produced without quality problems even for piece weights of several tons.

To obtain the properties which are optimal for a desired use, the proportions of the components of the alloy are usually varied, e.g. as described in more detail below. It has been found that the mechanical damping capacity which frequently alters greatly when the composition is varied can be optimized by means of a targeted fine tuning of the contents of the individual components of the alloy and set to higher values than if only the martensitic range were to be preferred for more readily reproducible damping properties, as is otherwise customary in the prior art.

For the targeted improvement of the mechanical damping, the martensite-austenite transformation temperatures or the associated ranges M_(S) to M_(F) and/or A_(S) to A_(F) are matched to a predetermined use or working temperature which will occur in the intended use of the alloy in a “component”. A high internal friction is also set as a result. The term “component” is intended to cover all conceivable practical use possibilities and include both individual parts and more complex multipart components, housings, machines and the like. Both the use temperature and the working temperature can be average temperatures, i.e. means of a working range or use range. If appropriate, both transformation temperature ranges, viz. the martensitic range and the austenitic range, can be used for matching to one relatively large working temperature range or two different working temperature ranges. Matching is achieved by variation of the proportions by weight of the abovementioned constituents of the alloy during melting of the alloy.

The properties of the alloy obtained by the process can be specifically matched to the respective intended use by means of the elements nickel, iron, cobalt, zinc, silicon, vanadium, niobium, molybdenum, chromium, tungsten, beryllium, lithium, yttrium, cerium, scandium, calcium, titanium, phosphorus, zirconium, boron, nitrogen, carbon. Thus, for example, an addition of nickel or silicon increases the corrosion resistance and strength properties. The elements iron, vanadium, niobium, molybdenum, chromium, tungsten, yttrium, cerium, scandium, calcium, titanium, zirconium, boron are of importance for achieving a fine-grade structure. Nitrogen and carbon together with transition elements improve the mechanical properties of the alloy obtained according to the invention. The aging resistance of the alloy both in the austenitic state and the martensitic state is increased by addition of cobalt. Beryllium and phosphorus protect the melt against oxidation. In addition, various combinations of the alloying elements enable a more or less strong influence to be exerted on the transformation temperatures of the alloy of the invention in order to optimally match the requirement profile for a specific application.

The alloy therefore preferably contains from 1 to 4% by weight of nickel. A preferred embodiment of the alloy contains from 11.6 to 12% by weight, preferably about 11.8% by weight, of aluminum. Furthermore, manganese contents in the range from 8 to 10% by weight in the alloy are preferred. The alloy can also preferably contain from 0.01 to 1% by weight of cobalt.

The microstructure of the cast alloy has relatively large cast grains and the grains are preferably made finer in order to achieve the optimal mechanical properties. Boron additions in the range from 0.001 to 0.05% by weight and/or chromium additions in the range from 0.01 to 0.8% by weight and/or iron additions of from 2 to 4% by weight are particularly effective for this purpose. In addition, grain refinement can also be effected by addition of rare earths in an amount of up to 0.3% by weight.

The alloy can also contain from 2 to 6% of zinc.

The alloys preferably have M_(S) temperatures of >0° C., without the invention being restricted thereto.

The invention gives a significant improvement in the damping properties since optimal setting of these properties while at the same time maintaining other desired properties has been made possible for the first time by the invention. The process of the invention enables the transformation temperatures in the material to be matched to the respective use conditions so that the specific damping capacity of the alloys of the invention at the intended use temperature is up to 80% and more.

The invention also encompasses a copper alloy which has a particular composition and comprises, as constituents of the alloy,

more than 4% by weight of manganese, more than 10% by weight of aluminum, from 0.01 to 0.8% by weight of chromium and, individually or together, from 0 to 18% by weight of one or more of the elements nickel, iron, cobalt, zinc, silicon, vanadium, niobium, molybdenum, chromium, tungsten, beryllium, lithium, yttrium, cerium, scandium, calcium, titanium, phosphorus, zirconium, boron, nitrogen, carbon, but each element in an amount of not more than 6%, and copper to 100% by weight.

This novel alloy for mechanically stressed components can additionally have the further specifications as indicated above and can likewise be obtained by matching the martensite-austenite transformation temperatures or the associated ranges M_(S) to M_(F) and/or A_(S) to A_(F) to a predetermined use or working temperature of the component, as described above.

In the case of existing HIDAMETs displaying martensitic phase transformations, it has been stated in the prior art that maximum damping occurs when the material is cooled from the austenitic state to close to the M_(S) temperature and when the material is heated from the martensitic state to the region of the A_(S) temperature. These damping maxima are not utilized in industry since the transformation temperatures of the material are difficult to reproduce using the existing processes. Apparently small changes in the chemical composition caused by oxidation or burning of the alloying elements result in shifts in the transformation temperatures which can be more than 100° C. For this reason, it has hitherto not been possible to set the M_(S) or A_(S) temperature reproducibly to within ±10° C. even by very precise formulation of the charge and carrying out melting with great care. Attainment of the damping maximum is therefore deliberately dispensed with in favor of smaller but more reproducible damping values in the purely martensitic state in the production of conventional HIDAMETs.

This disadvantage is overcome by the invention.

Experiments carried out by the inventor show that addition of copper increases the transformation temperatures. Additions of other alloying elements reduce the transformation temperatures. A particularly strong effect on the martensitic transformation temperatures can be achieved by addition of aluminum and manganese. In a preferred embodiment, correction of the transformation temperatures is therefore achieved during melting by addition of copper or aluminum. Due to the high melting point of manganese and the high affinity for oxygen, addition of aluminum is preferred over addition of manganese for reducing the transformation temperatures.

In the case of the alloy of the invention, the maximum values for the specific damping capacity occur when the alloy is cooled from the austenitic state to a temperature in the range from M_(S) to M_(F) and when the alloy is heated from the martensitic state to a temperature in the range from A_(S) to A_(F).

The temperature in the middle of the martensitic or austenitic range of the phase transformation should therefore be very close to the use temperature of components composed of the alloy of the invention. The invention therefore makes it possible to produce alloys for specific predetermined use or working temperatures or temperature ranges, which are then particularly suitable for particular applications and components.

The precise setting of the transformation temperatures is carried out using a sample which is taken during the melting process and allows express monitoring of the transformation temperatures for the liquid alloy. As sample for express monitoring, preference is given to using a cast wire which is drawn from the melt with the aid of a fused silica tube in which a subatmospheric pressure is generated. The transformation temperatures can be determined on this sample either in the cast state or after heat treatment, depending on the intended use, by means of known experimental methods for detecting phase transformations.

The transformation temperature of the sample is preferably determined by calorimetry, dilatometry, measurement of the electrical conductivity, optical microscopy or measurement of the acoustic emission.

Based on the results of the examination of the express sample, a direct correction of the chemical composition of the melt is made, preferably by means of copper or aluminum as described above. The process of the invention thus makes it possible to set the transformation temperatures in the material so that the alloy achieves the maximum possible damping capacity at the desired use temperature. Efficient matching of the material to the respective use conditions is therefore basically ensured.

The martensitic transformation can also be induced in a defined temperature range by means of externally applied stresses. In this case, the transformation temperatures in the material increase linearly with the stress. This increase in the transformation temperatures has to be taken into account in the production of components from the alloy of the invention if mechanical stresses are to be expected there.

In addition to the abovementioned influencing factors, the damping maximum is also influenced to a considerable extent by the microstructure of the alloy, with larger grains leading to better damping properties. The grain size of the alloy can be set by means of suitable alloying measures so that an optimal compromise between the damping capacity and the mechanical properties is achieved for each specific application.

It has also been found that an improvement in the damping properties can be achieved by means of heat treatment. Heating at temperatures of from 650° C. to 950° C. with subsequent cooling or quenching in liquid or gaseous media, e.g. air, liquid nitrogen, water, a salt bath or oil, has been found to be particularly effective. The temperature of the quenching medium should preferably be above the M_(S) temperature in order to avoid uncontrollable shifts in the transformation temperatures in the material. The aging sensitivity of the transformation temperatures can, according to the invention, be reduced by means of additional heat treatment of the quenched alloy at a temperature of from 150° C. to 250° C. The duration of such a heat treatment is advantageously from 5 to 120 minutes.

In the case of large and solid castings composed of the alloy of the invention which cannot be subjected to heat treatment and quenching, a martensitic microstructure can, according to a further aspect of the invention, be produced in the outer layer by laser remelting. Here, the outer layer takes on the damping role without the entire component having to be subjected to costly heat treatment. In the production of such castings, the transformation temperatures of the alloy are set during melting by means of express monitoring so that, taking into account the cooling conditions during laser remelting, the transformation temperatures in the outer layer correspond to the use temperature of the component.

The alloys obtained by the process of the invention can be used particularly advantageously for reducing vibrations and for noise damping on mechanically stressed components, especially for ships, propellers, machine housings, in particular pump housings, generator housings, vibrating machines, precision apparatuses, electronic instruments, tools which are subjected to vibrations and/or impacts during operation or produce these, in particular for punches, dies, machine hammers, lathe tools and milling tools.

The invention is illustrated below with the aid of an example.

EXAMPLE

Noise-damping compressor housings or various hydraulic components can be produced using an alloy which displays its maximum damping properties at a temperature of about 120° C.

For this purpose, the following alloy was produced in air in an induction furnace:

-   -   Basic composition:     -   84% by weight of copper     -   12% by weight of aluminum     -   4% by weight of manganese

Express Sampling:

For the express monitoring of the transformation temperatures, the following method was developed: A cast wire having a length of from 10 to 150 mm (preferably from 15 to 100 mm) and a cross-sectional area of from 0.2 to 7 mm², preferably from 0.7 to 3.2 mm², serves as sample. This is drawn from the melt by means of a fused silica tube in which a subatmospheric pressure is produced. Known detection methods can be applied directly and very quickly to this sample. In a preferred method used here, too, the acoustic emission is monitored over a temperature profile.

The first sample for the express monitoring of the transformation temperatures on the melt having the basic composition gave A_(F)=100° C.; A_(S)=52° C.; M_(S)=68° C. and M_(F)=15° C.

The transformation temperatures of this melt were corrected to higher values by addition of copper. Values determined on the subsequent express sample were A_(F)=145° C., A_(S)=74° C.; M_(S)=102° C. and M_(F)=43° C. These transformation temperatures are well-suited to achieving maximum damping values at 120° C. The melt was cast into an ingot mold which had been preheated to 300° C. Specimens for damping measurements were cut from the castings obtained. The damping behavior was characterized by means of the specific damping capacity. The internal friction was measured at a flexural vibration frequency of 0.1 Hz with a constant heating rate and cooling rate (1 K/s). The 2980 DTMA V1.7B instrument from TA Instruments was used for these purposes. The internal friction is measured as the phase angle between mechanical stress and strain. The damping behavior was characterized by means of a specific damping capacity given by the formula

spec. damping capacity=2π tan φ.

The damping behavior of the alloy produced in this way is shown in FIG. 1.

FIG. 1: Development of the specific damping capacity of the alloy from the example, recorded for one heating and cooling cycle

FIG. 1 shows a curve recorded for the above-described example. The specific damping capacity in % is plotted against the temperature in 0° C. The temperatures were raised from below zero to 200° C. and brought back again in a heating and cooling cycle. As can be seen, significantly higher damping is achieved in the austenitic range than in the martensitic range for the illustrative alloy, so that the restriction to martensitic structures which is frequently applied in the prior art has to lead to significant disadvantages in terms of the alloy properties.

The illustrative alloy attains its maximum damping properties at a temperature of 120° C. and thus successfully achieves the object set. The damping which can be achieved is above 70%. 

1. A process for producing a Copper alloy having specifically improved mechanical damping for mechanically stressed components, which comprises, as constituents of the alloy, from 2 to 12% by weight of manganese, from 5 to 14% by weight of aluminum and, individually or together, from 0 to 18 by weight of one or more of the elements nickel, iron, cobalt, zinc, silicon, vanadium, niobium, molybdenum, chromium, tungsten, beryllium lithium, yttrium, cerium, scandium, calcium, titanium, phosphorus, zirconium, boron, nitrogen, carbon, but each element in an amount of not more than 6%, and copper to 100% by weight, characterized in that a) a composition for the alloy is selected and the constituents are melted in a Customary way at a suitable temperature, b) during this melting, at least one of the marten-sjtjc and austenitic transformation temperatures M_(S), M_(F), A_(S) and A_(F) is determined on a sample taken from the melt, C) these transformation temperatures are increased or reduced on the basis of a predetermined use or working temperature of the component by targeted addition of at least one constituent of the alloy and thus matched to the use or working temperature, d) the new transformation temperatures and, if appropriate, ranges are checked by means of a further sample and e) the alloy is cast into the desired mold.
 2. The process as claimed in claim 1, Characterized in that the steps c) and d) are repeated as often as necessary.
 3. The process as claimed in claim 1, characterized in that correction of the transformation temperatures is carried out during melting by addition of copper or aluminum.
 4. The process as claimed in claim 1, characterized in that the transformation temperatures are set so that the temperatures in the middle of the martensitic or austenitic range of the phase transformation are very close to the predetermined use or working temperature.
 5. The process as claimed in claim 1, characterized in that the alloy in the form of a Shaped part obtained initially by Casting or forging and if appropriate forming is subjected to heat treatment at temperatures of from 650° C. to 950° C. and subsequent cooling or quenching in liquid or gaseous media, in particular air, liquid nitrogen, water, a salt bath or oil.
 6. The process as claimed in claim 5, characterized in that the temperature of the quenching medium is above the M_(S) temperature of the alloy.
 7. The process as claimed in claim 1, characterized in that the alloy in the form of a shaped part obtained initially by casting or forging and if appropriate forming is heat treated/aged at a temperature of from 100 to 300° c. for from about 5 to 120 minutes.
 8. The process as claimed in claim 1, characterized in that the alloy is subjected to one or more thermal cycles between the austenitic state and the martensitic state and back.
 9. The process as claimed in claim 1, characterized in that heat treatment of the outer layer of a shaped part obtained from the alloy by casting or forging and if appropriate forming is effected by means of laser remelting of the outer zone.
 10. The process as claimed in claim 1, characterized in that the sample for quick monitoring of the transformation temperatures is taken by means of a fused silica tube in which a subatmospheric pressure is produced.
 11. The process as claimed in claim 1, characterized in that the transformation temperatures are determined on the sample by calorimetry, dilatometry, measurement of the electrical conductivity, optical microscopy or measurement of the acoustic emission.
 12. The process as claimed in claim 1, characterized in that the damping behavior is additionally influenced by targeted alteration of the grain size.
 13. A copper alloy, in particular for mechanically stressed components, having specifically improved mechanical damping, which comprises, as constituents of the alloy, from >4 to 12% by weight of manganese, from >10 to 14% by weight of aluminum, from 0.01 to 0.8% by weight of chromium and, individually or together, from 0 to 18% by weight of one or more of the elements nickel, iron, cobalt, zinc, silicon, vanadium, niobium, molybdenum, chromium, tungsten, beryllium, lithium, yttrium, cerium, scandium, calcium, titanium, phosphorus, zirconium boron, nitrogen, carbon, but each element in an amount of not more than 6%, and copper to 100% by weight.
 14. The copper alloy as claimed in claim 13, characterized in that the alloy contains from 1 to 4% by weight of nickel.
 15. The copper alloy as claimed in claim 13, characterized in that the alloy contains from 11.6 to 12% by weight, preferably about 11.8% by weight, of aluminum.
 16. The copper alloy as claimed in claim 13, characterized in that the alloy contains from 8 to 10% by weight of manganese.
 17. The copper alloy as claimed in claim 13, characterized in that the alloy contains from 2 to 4% by weight of iron and/or from 0.001 to 0.05% by weight of boron.
 18. The copper alloy as claimed in claim 13, characterized in that the alloy contains from 0.01 to 1% by weight of cobalt.
 19. The copper alloy as claimed in claim 13, characterized in that the alloy contains from 0.01 to 0.3% by weight of rare earths.
 20. The copper alloy as claimed in claim 13, characterized in that the alloy contains from 2 to 6% by weight of zinc.
 21. (canceled)
 22. (canceled) 